The present invention relates to a receiver which can receive a high definition TV signal and more particularly to a high definition TV signal receiver which can receive a high definition TV signal which is compressed to a band width which is the same as that of a TV signal of the standard system such as the NTSC system and a TV signal of the standard system even when they are multiplexed and transmitted within the co-channel.
Furthermore, the present invention relates to a high definition TV signal receiver which can selectively receive a high definition TV signal and a standard TV signal and relates to a high definition TV signal receiver which can share and receive a high definition TV signal which is compressed to a band width which is the same as that of a TV signal of the standard system and a TV signal of the standard system (a TV signal of not only the NTSC system but also another standard system which is modulated in amplitude is included).
As television broadcasting and CATV broadcasting have been expanded recently, broadcasting channels are being multiplexed. In correspondence with it, to reduce image interferences and reception interferences due to leakage of a local oscillation signal even at the time of multi-channel reception, a receiver of the double super-heterodyne system is used.
However, the aforementioned prior art is used to receive a TV signal of the standard system such as the NTSC system and reception of a signal which is digitally modulated such as a high definition TV signal is not taken into account. Multiplexing and transmission of a TV signal of the standard system and a high definition TV signal in the co-channel are neither taken into account.
An object of the present invention is to provide a high definition TV signal receiver which can selectively receive one of a TV signal of the standard system and a high definition TV signal.
To accomplish the above object, the present invention uses the double super-heterodyne system as a basic constitution so as to receive a high definition TV signal, uses a band pass filter having a flatness in pass band characteristics and a small deviation of group delay characteristics which prevent the demodulation of a high definition TV signal from degradation as a first intermediate frequency filter, uses a high definition TV signal filter (surface acoustic wave filter, etc.) as a second intermediate frequency filter, installs a third mixer for converting a high definition TV signal to a third intermediate frequency signal, and installs a high definition TV signal demodulator in the demodulation section.
To share and receive a high definition TV signal and a TV signal of the standard system, the present invention uses the double super-heterodyne system as a basic constitution, uses a band pass filter having a flatness in pass band characteristics and a small deviation of group delay characteristics which prevent the demodulation of a high definition TV signal from degradation as a first intermediate frequency filter, uses a high definition TV signal filter and a filter (surface acoustic wave filter, etc.) for a TV signal of the standard system such as a TV signal of the NTSC system as a second intermediate frequency filter, installs a third mixer for converting a high definition TV signal to a third intermediate frequency signal, installs a high definition TV signal demodulator in the demodulation section, and an AM demodulator for a TV signal of the standard system in the demodulation section.
Furthermore, to share and receive a high definition TV signal and a TV signal of the standard system, the present invention uses the double super heterodyne system as a basic constitution, uses a band pass filter having a flatness in pass band characteristics and a small deviation of group delay characteristics which prevent the demodulation of a high definition TV signal from degradation as a first intermediate frequency filter, uses a high definition TV signal filter as a second intermediate frequency filter, installs a third mixer for converting a high definition TV signal to a third intermediate frequency signal, and installs a common demodulator for a high definition TV signal and a TV signal of the standard system in the demodulation section.
The present invention having the aforementioned constitution can selectively select a TV signal of the standard system and a high definition TV signal even when they are multiplexed and transmitted in the co-channel or even when they are transmitted independently.